Solubilization of Coal and Bioconversion of Coal to Methane and Other Useful Products

ABSTRACT

Coal is contacted, or treated, with at least one aromatic alcohol and/or cycloaliphatic alcohol to solubilize at least a portion of the treated coal. The treated coal is optionally bioconverted to produce one or more hydrocarbons, such as methane.

This application claims priority of U.S. Provisional Application 61/283,890, filed 10 Dec. 2009, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the solubilization of coal and the bioconversion of coal to methane and other useful products.

BACKGROUND OF THE INVENTION

Organic solvents such as carbon disulfide, tetrahydrofuran, pyridine, tetracyanoethylene, N-methyl-2-pyrrolidinone have been used separately and in combination to extract coal components. The extraction of coals with pyridine is also commonly performed in the coal industry.

When biomass is buried and subjected to pressure and temperature under increasingly anoxic conditions, the biomass is converted to peat, and then to low-rank coal, known as lignite. Lignite coal contains partially coalified plant materials, including lignins. As coalification increases, the oxygen content of the coal decreases, the carbon content increases, and the amount of lignin decreases.

Also as the biomass undergoes the coalification process, bacteria and fungi may become entrained or may enter the biomass deposit, that are able to convert the carbon in the biomass or lignite or coal to methane, carbon dioxide and other products. The conversion of the coal is a slow and incomplete process.

The present invention is directed to the treatment of coal to solubilize coal and in a preferred embodiment to treat coal to render coal more susceptible to conversion by bacteria and fungi to methane and other useful products.

SUMMARY OF THE INVENTION

One aspect of the present invention is directed toward a method of solubilizing coal by treating coal with one or more aromatic alcohols and/or cyclic aliphatic alcohols by contacting coal with such one or more alcohols to solubilize at least a portion of the coal.

In one aspect, the method includes treating coal with a mixture of (i) water and (ii) one or more aromatic alcohols and/or cycloaliphatic alcohols, under conditions effective to solubilize at least a portion of the coal.

Another aspect of the present invention is directed toward a composition comprising solubilized alcohol derivatives of coal, preferably derivatives useful in energy production, such as the formation of fuels and the like.

A further aspect of the present invention is directed toward a bioconversion method wherein coal is treated with one or more aromatic alcohols and/or cycloaliphatic alcohols and a bioconversion agent to convert coal; e.g., to methane and/or other products.

In one embodiment, one or more aromatic and/or cycloaliphatic alcohols is injected into a coal-bearing formation, such as by use of a well, in order to solubilize coal contained therein, either for the purpose of effecting extraction of valuable energy-yielding components of the coal or for enhancing bioconversion of the coal to methane and other useful products. Such a formation may contain microorganisms, such as anaerobic bacteria, and/or facultative anaerobe, and/or acetogens and/or methanogens or even fungi, that are capable of bioconverting the coal into other products. Alternatively, such microorganisms may be added to the formation or well so as to effect such bioconversion.

In one embodiment, the one or more aromatic and/or cycloaliphatic alcohols are injected into a coal-bearing formation continuously or in steps in order to solubilize coal and enhance bioconversion of the coal to methane and other useful products.

In one example of a method of the invention the aromatic and/or cycloaliphatic alcohol, or alcohols, are heated and then injected into a coal-bearing formation to solubilize coal contained therein. In a further example, such injection is carried out in combination with sonication to solubilize coal.

The coal useful in the methods of the invention includes all forms of coal, processed or unprocessed, such as coal that has been mined as well as coal present in a subterranean formation.

Definitions

As used herein, coal refers to any of the series of carbonaceous fuels ranging from lignite to anthracite. The members of the series differ from each other in the relative amounts of moisture, volatile matter, and fixed carbon they contain. Of the coals, those containing the largest amounts of fixed carbon and the smallest amounts of moisture and volatile matter are the most useful to humans. The lowest in carbon content, lignite or brown coal, is followed in ascending order by sub-bituminous coal or black lignite (a slightly higher grade than lignite), bituminous coal, semibituminous (a high-grade bituminous coal), semianthracite (a low-grade anthracite), and anthracite.

As used herein, the term “aromatic alcohol” means an organic compound having the formula ROH, wherein R is a substituted or unsubstituted aromatic group, which the aromatic group may be a monocyclic ring or a fused ring. In one embodiment, the aromatic group R is unsubstituted. In another embodiment, R is substituted with one or more of a hydrocarbon group and/or an —OH group(s). In some embodiments, the —OH is present on the aromatic ring, or is present in a substituent of said ring or both.

As used herein, the term “cycloaliphatic alcohol” means an organic compound having the formula R₁OH, wherein R₁ includes a substituted or unsubstituted cycloaliphatic group. In one embodiment, the substituent group may be one or more of —OH and or an aliphatic hydrocarbon. Preferred cycloaliphatic alcohols include, but are not limited to, cyclopropanols, cyclobutanols, cyclopentanols, cyclohexanols, and cycloheptanols.

As used herein, the term “solubilizing” or “solubilized” when used with reference to coal” means that after treatment with the aromatic and/or cycloaliphatic alcohol, the solid content of the coal has been reduced. Without limiting the foregoing and/or limiting the invention, it is believed that such reduction in solid content is achieved by (i) the breaking of bonds in the coal matrix resulting in chemical breakdown of portions of the coal and/or (ii) cleaving of bonds holding carbon layers together. Thus, the solubilization of the coal may involve one or more of a chemical break-down of the coal and/or cleaving of bonds.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the present invention is directed toward a method of treating coal. The method includes contacting coal with one or more aromatic alcohols and/or one or more cycloaliphatic alcohols.

In certain embodiments, coal is contacted with one aromatic alcohol and/or cycloaliphatic alcohol. In some embodiments, a mixture of aromatic alcohol and/or cycloaliphatic alcoholics is used.

The coal may be lignite or any form or rank of coal, ranging from brown coal to anthracite, based on increasing carbon content.

The coal is contacted with the alcohol under conditions effective to solubilize at least a portion of such coal.

In a non-limiting embodiment, the treating is effected at temperatures in the range 0 to 300° C., including temperatures of 0 up to 200° C., preferably at a temperature of 10 to 200° C.

Without limiting the invention, the treating may be effected at a variety of pH conditions that include pH ranges 2 to 12, 3 to 11, 5 to 10, and the like, or may lie in the acid or alkaline range, such as 1 to 6, 2 to 5, or 3 to 4, or in the range 8 to 13, or 9 to 12, or 10 to 11.

Without limiting the invention, the treating may be effected at a variety of pressure conditions that include atmospheric pressure, above atmospheric pressure, or below atmospheric pressure. For example, in treating coal deposits in situ, the pressure may be the pressure prevailing in the deposit or at an elevated pressure by controlling the pressure at which liquid is introduced into the well. Those skilled in the art are aware of how to optimize the conditions for treating the coal based on the teachings of the invention.

The alcohols which may be used in the invention include substituted and unsubstituted aromatic and cycloaliphatic alcohols. In one embodiment, one or more —OH groups of said alcohol are directly attached to an aromatic or cycloaliphatic ring, while in other examples one or more —OH groups are part of a substituent attached to an aromatic or cycloaliphatic group. In some examples, an —OH group is attached to both the ring and to a substituent of the ring. Preferred alcohols include cyclopropanols, cyclobutanols, cyclopentanols, cyclohexanols, cycloheptanols, benzenediols or benzyl alcohol, catechol (or pyrocatechol), 1,2-dihydroxybenzene; phenol, resorcinol, vanillyl alcohol, hydroquinone, cresol, or mixtures of any of these. In accordance with the invention, said alcohol may or may not be mixed with water. In one preferred embodiment, the alcohol is used in admixture with water.

In specific embodiments, the alcohols of the invention are aryloxy alcohols, wherein an —OH is attached to an aryl group, such as phenyl. The alcohols useful in the methods of the invention are not limited to alcohols possessing a single —OH radical but include alcohols possessing multiple —OH groups. In a preferred embodiment, the —OH radical is attached directly to a cycloaliphatic or aromatic ring and more than one such —OH group may be attached to said ring.

As noted above, where the cycloaliphatic or aromatic ring is substituted with one or more other radicals, such as alkyl radicals, such an alcohol may possess an —OH attached directly to the ring and an —OH attached to one or more of said substituents. Where the ring is a phenyl ring, a phenol is a preferred embodiment, more preferably hydroxyphenol, where the additional —OH radical is attached directly to the phenolic ring. One such preferred embodiment is catechol (or C₆H₄(OH)₂).

The method of the present invention may also include treating coal with one or more alcohols of the type hereinabove described to solubilize at least a portion of the coal in which the combination of coal and treating agent is subjected to sonication during or after the treating or contacting, which sonicating may be part of, the solubilizing process or may be used only to form a more uniform product that results from the treating.

In accordance with one embodiment of the invention, coal is treated to solubilize at least a portion of the coal as hereinabove described as part of a process for biconverting the coal to a product that includes methane. In such a process, the bioconversion may be effected in conjunction with such treating or at least a portion of product from such treating may then be subjected to bioconversion to produce a product that includes methane.

The bioconversion (either in conjunction with solubilization or by bioconverting at least a portion of product recovered from the solubilization with or without prior treatment of such recovered product) is effected by use of a bioconversion agent effective for converting coal to a product that includes methane.

In certain embodiments, the bioconversion is effected by one or more bioconversion agents. The bioconversion agents may be facultative anaerobes, such as those of the genus Staphylococcus, Escherichia, Corunebacterium and Listeria, acetogens, for example, those of the genus Sporomusa and Clostridium, and methanogens, for example, those of the genus Methanobacterium, Methanobrevibacter, Methanocalculus, Methanococcoides, Methanococcus, Methanocorpusculum, Methanoculleus, Methanofollis, Methanogenium, Methanomicrobium, Methanopyrus, Methanoregula, Methanosaeta, Methanosarcina, Methanophaera, Methanospirillium, Methanothermobacter, and Methanothrix. The bioconversion agents may also be eukaryotes, such as fungi.

The bioconversion is operated under conditions effective to bioconvert the alcohol treated coal and/or products obtained therefrom as a result of the alcohol treatment to hydrocarbons and carbon dioxide. Useful bioconversion agents include facultative anaerobes, acetogens, methanogens and fungi as described elsewhere herein. Suitable bioconversion includes formation of hydrocarbons such as methane, ethane, propane; and carboxylic acids, fatty acids, acetate, carbon dioxide.

In accordance with an embodiment of the invention, wherein coal is bioconverted by a combination of solubilization of coal by use of one or more aromatic and/or cycloaliphatic alcohols and bioconversion of the treated coal and/or coal solubilization product, one or more chemicals and/or nutrients and/or vitamins and/or minerals may be used in the process to promote bioconversion of the treated coal and/or coal solubilization products. Such materials may be employed as a supplement for growth and/or to enhance the bioconversion action of the organisms used as a bioconversion agent.

In bioconverting coal in accordance with one embodiment of the invention, the coal is present in a coal seam or deposit and the solubilization and bioconversion is effected in situ. Bioconversion of treated coal in situ may be accomplished by an appropriate combination of bacteria, for example, one that includes two or more of facultative anaerobes, acetogens, methanogens; and fungi, especially those of a genus recited elsewhere herein. Such combination may be endogenously present in the coal deposit and/or may be added to the coal deposit as part of the solubilization and bioconversion process. In specific embodiments, one or more nutrients, vitamins, minerals, metal catalysts and other chemicals are added to the coal deposit to promote the growth of the bacteria or fungi.

The aromatic alcohols and/or cycloaliphatic alcohols used in the process may be injected into a coal deposit as part of the overall procedure for bioconverting coal.

The herein described methods and examples in no way limit the invention to the embodiments described herein and that other embodiments and uses will no doubt suggest themselves to those skilled in the art. 

1. A method of treating coal comprising: contacting coal with at least one member selected from the group consisting of aromatic alcohols and cycloaliphatic alcohols to solubilize at least a portion of the coal.
 2. The method of claim 1, wherein the coal is fully solubilized as a result of said contacting.
 3. The method of claim 1, wherein the coal is partially solubilized as a result of said contacting.
 4. The method of claim 1, wherein the coal is selected from the group consisting of lignite, brown coal, sub-bituminous coal, bituminous coal, anthracite, and combinations thereof.
 5. The method of claim 1, wherein said contacting is carried out at a temperature of 0 to 300° C.
 6. The method of claim 1, wherein said contacting is carried out at a temperature of 10 to 200° C.
 7. The method of claim 1, wherein said contacting is carried out at a pH range of 5 to
 10. 8. The method of claim 1, wherein said at least one member is an aromatic alcohol.
 9. The method of claim 1 further wherein the coal and said member is subjected to sonication during the contacting.
 10. The method of claim 1 further comprising treating with one or more bioconversion agents during or after said treating with said member.
 11. The method of claim 10 further comprising adding nutrients, vitamins, minerals, and metal catalysts before or during the contacting.
 12. The method of claim 10, wherein the bioconversion agent is at least one member selected from the group consisting of facultative anaerobes, acetogens, methanogens and fungi.
 13. The treated blend formed by the method of claim
 1. 14. A composition comprised of the solubilized aromatic or cyclic alcohol derivatives of coal.
 15. A bioconversion method comprising: contacting the treated coal of claim 1 with a bioconversion agent to bioconvert the coal.
 16. The method of claim 15 wherein the bioconversion agent comprises any or all of facultative anaerobes, acetogens, methanogens and fungi.
 17. The method of claim 15 wherein said bioconversion results in the formation of methane. 